border-1px($color)
  position :relative
  &:after
    display:block
    position:absolute
    left:0
    bottom:0
    width:100%
    border-top: 1px solid $color
    content: ''

border-no()
  &:after
    display:none


bg-image($url)
  background-image :url($url+"@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(-webkit-min-device-pixel-ratio: 3)
    background-image :url($url+"@3x.png")
